Every year nearly two million people, half of them children, die from diseases related to contaminated drinking water and many more become ill from water that could easily be purified.

The “compartment bag test” (CBT) fills a developing world need, to provide an accurate, portable evaluation of household water supply safety from disease-causing bacteria.

The device is a plastic bag divided into five differently sized internal compartments that split the 100-ml water sample. Overnight, the CBT can accurately measure the presence and concentrations of E. coli fecal bacteria.

The portable, self-contained test is lightweight and requires no electricity, additional equipment, a cold chain or a laboratory to accurately measure the water quality on site.

The surveyor labels the bag, takes a water sample from the usual household supply point, and mixes it with a bacteriological culture medium. The sample is poured into the bag where it spreads through the compartments; the bag then incubates overnight. E. coli contamination is present when the water sample in a compartment turns blue, and the number and volumes of the blue compartments indicate the bacteria levels as a measure of risk.

The surveyor then follows up with information for households where the water supply is contaminated, showing them methods to purify the water by filtration, chlorination, boiling, or standing in the sun.